Why do neural networks based AI players still require extensive search techniques?
It is not very accurate to say that AI players requires extensive search while humans don't. Rather, it is a question of degree. 

AIs do a lot more calculating, because that's what computers are good at. 

Human intuition is much more powerful than a neural network can currently hope to match, because it is much more integrated into a world of knowledge about the game, it uses orders of magnitudes more neurons and it is not a static thing that just provides a move.

But if a human player stops calculating ahead his playing strength will drop very significantly. This can be seen by assessing the performance in games with short time controls: The less time you have the less calculation is happening, your intuition however is fast.

If you take out the search component of AlphaGo it would still play quite strongly, probably at a low dan level. Of course that is also far below its strength. 

So, search is always an important component of playing strength, just more so for machines.